Ropinirole was developed as a drug which conquers the limit associated with L-Dopa therapy, and has been used for treating Parkinson's disease. Further, transdermal preparations containing ropinirole have been studied owing to the avoidance of adverse reactions on the stomach and intestines and the easy removal in case adverse reactions occur (Patent Documents 1 and 2).
On the other hand, the drug is distributed in the market in the form of an acid adduct salt from the viewpoints of the handleability and stability thereof. When a drug in the form of an acid adduct salt is directly applied for transdermal administration or the like, it is generally known that the absorbability tends to be decreased, but also known that a free form of a drug is preferred in terms of the absorbability.
In Patent Document 3, a technique wherein a drug acid adduct salt is used as a starting material for producing a transdermal preparation and the drug acid adduct salt is neutralized (desalted) in the preparation during the production or after the production so that a free form can be absorbed at the time of transdermal administration.    Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2001-518058    Patent Document 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. H11-506462    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2007-16020